Hitherto, a button type alkaline cell is manufactured by fabricating a negative electrode can by using metallic molds such as a die, a punch and a blank holder made from tool steel, high speed steel or cemented carbide and by combining it with other components such as a positive electrode compound, a negative electrode compound, a separator, a positive electrode can, a gasket and a alkaline electrolyte.
As raw materials of the negative electrode can of the button type alkaline cell, an Ni--SUS--Cu clad material or a material in which Ni is plated on the side opposite from Cu which becomes the inner surface of the negative electrode can on a laminated material of Cu and SUS or Cu and a deep drawing steel is used. The negative electrode can is fabricated by working the raw material using a die made from tool steel or cemented carbide. The button type alkaline cell is manufactured by combining this negative electrode can with the other components such as the negative electrode compound mainly composed of zinc, the positive electrode compound mainly composed of silver oxide, the separator, the electrolyte, the positive electrode can and the gasket.
However, the button type alkaline cell using the negative electrode can manufactured by using the prior art die, in which tool steel or cemented carbide is used for the part which contacts with the Cu surface, generates gas from the Cu surface when the negative electrode zinc contacts with the alkaline electrolyte and when part of the electrolyte decomposes. It is because Fe of the tool steel, Co or Ni used as a binder of the cemented carbide or W which is the base material of the cemented carbide is transferred and adheres on the Cu surface, i.e. the inner surface of the negative electrode can, during working of the negative electrode can, though it is a very small amount. The generation of gas leads to the exhaustion of the negative electrode compound within the button type alkaline cell, thus deteriorating the self-discharge characteristic of the cell.
Although the gas may be suppressed from generating by containing mercury within the negative electrode compound because the degree of generation of gas may be reduced as the mercury covers the Cu surface, there is apprehension that the environment might be contaminated by the mercury contained within the disposed cells.
Although it has been attempted to reduce the amount of mercury by fully cleaning the negative electrode can or by adding indium and bismuth in order to reduce the amount of mercury contained within the button type alkaline cell and to maintain the effect of suppressing the generation of gas (e.g. Japanese Patent Laid-Open Nos. Hei. 8-31428, Hei. 8-130021 and others), it is difficult to prevent the gas from generating from the inner surface of the negative electrode can.